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Marijuana DUI: Understanding Illinois Law

Posted on in DUI Drugs

Illinois defense lawyerThe effect of alcohol consumption on the ability to drive safely has been studied intensely for over 60 years. Scientists have developed tests of blood alcohol concentration (BAC), including breathalyzers and blood tests, that are accurate enough to be fully accepted by American courts. Scientific studies have proven that alcohol impairment begins with the first drink; that the higher a person’s BAC level is, the more impaired their driving is; and that .08 is a level at which driving is so impaired as to pose a significant danger to public safety.

But when it comes to marijuana, such conclusive research does not yet exist. Yes, the level of THC, marijuana’s main psychoactive component, in the blood can be measured. But, different from alcohol, THC can be present in the blood long after its psychoactive effect has worn off. There is currently no test that can differentiate “active” THC that would impair driving from “inactive” THC that would not. Nor is there clear and convincing research showing what level of THC results in impaired driving, or widespread agreement on what the legal limit should be.

So how can Illinois arrest, much less convict, people of driving under the influence of marijuana?

Current Illinois Law Governing Marijuana DUI

Prior to 2016, the legal limit of THC for Illinois drivers was zero. Under that law, a person could be convicted of driving under the influence even if they had not smoked or consumed marijuana in any form for days or even weeks, and their driving was not actually impaired by THC.

In 2016, Illinois changed the legal limit for THC to 5 nanograms or more per milliliter of whole blood or 10 nanograms or more of THC per milliliter of other bodily substance (e.g., saliva). While there is little, if any, scientific basis for setting the legal limit for THC at this level, this is the current law in Illinois and a couple of other states.

Note that the law requires the blood test for THC to be conducted within two hours of driving. There is no specific time requirement like this for alcohol testing. Saliva testing is still in the early stages of development and has not yet been used as evidence in Illinois courtrooms.

A driver can refuse the blood test, but the police can then get a warrant allowing them to forcibly draw blood for testing. Just remember that refusing the test carries a longer statutory summary suspension than voluntarily submitting and being over the legal limit.

In addition to chemical testing, the police can and will use their observations of driving behavior (e.g., weaving across traffic lanes) as well as the standardized field sobriety tests (e.g., the one-legged stand and the walk-and-turn) as evidence of driver impairment, regardless of the form of intoxicant. Police can also cite their observations of the smell of marijuana about the driver or the presence of cannabis in the vehicle.

DUI by Illinois Medical Marijuana Cardholders

The legal limit for THC does not apply if the driver has a medical cannabis card. But a cardholder can still be charged with and convicted of DUI if they are judged to be impaired based on their driving behavior and their performance on field sobriety tests. While other drivers may refuse to perform field sobriety tests, medical marijuana cardholders cannot refuse.

Marijuana DUI Defense Attorney in Oak Brook

If you have been arrested for DUI—whether for alcohol, marijuana, or some other intoxicant—know that you have options, even if you tested over the legal limit. To determine the best strategy based on the circumstances of your specific case, consult an experienced DuPage County DUI defense lawyer before making any decisions. The attorneys at McMahon Law Office will diligently investigate all the circumstances of your case and work aggressively to get you the best possible outcome. For a free consultation, call 630-953-4400.








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